The long term goal of the proposed project is to develop a theoretical account of the processes underlying diagnostic classification learning in medical problem solving. The research is aimed at analyzing the cognitive processes associated with acquiring, accessing, and updating diagnostic categories. The proposed experiments are in three main areas. One focus in on the use of base rate or prevalence information where this base rate information derives from experience in classifying cases. A second objective is to study learning variables associated with acquiring and using diagnostic categories. For example, one set of studies examines how abstract information is integrated with experience with examples or cases to determine classification performance. The third area of interest is in the relationship between abstract category structures and diagnostic reasoning processes in determining what is learned (the nature of inductive generalizations) about diagnostic categories. All of the work will make use of classification learning research drawn from cognitive psychology.